There are theistic Satanists and atheistic Satanists.
The former version identifies with various incarnations of evil associated with different religions including Christianity, Hinduism, and Egyptian mysticism. They celebrate and literally believe in Satan, Hades, Shaitan, Set, etc.
The latter sees the figure of Satan as allegorical, not literal. They don't react as strongly towards religions because they don't actually believe in angels and demons. To them, it's all symbolic and philosophical.
All Satanists, theists or atheists, basically encourage pure, truthful, unrestrained, righteous hedonism. Do what you want. Be free, but do not tread upon the freedom of others and accept responsibility for your actions.
It ain't a bad school to study in. It's not Luciferianism, but it's a big step in the right direction.